Composition / Accessory
Minerals / Magnetic
Susceptibility / Field Relationships and Distribution
Crystal-rich volcanic sandstone and
Mudstone / massive to bedded; crystals and minor lithic fragments in a sand - mud matrix (closed framework) / 10-80% plg to 1mm; minor hbl+pyx; subrounded-subangular volcanic clasts to 5mm; pebble horizons / fine- to medium- grained sand, silt and micro-crystalline material / An 95 to 45 for the larger crystals,
normal- zoned locally / 3-5% mt to 0.2mm / 5000-7000
x 10-5 SI;
0-200 x 10-5 SI
where epidote altered / SantongValley and northern tributaries to Batu Hijau, where it is overlain by the volcanic lithic breccia sequence
Crystal-rich volcanic lithic breccias / massive and poorly sorted; minor graded bedding fines upward locally / 0-20% subrounded-subangular andesitic clasts < 6cm; matrix supported / 20-50% plg to 2mm; 2-5% hbl + pyx to 4mm; plg-rich mud matrix / An 95 to 40,
normal-zoned
locally / 3-7% mt and ilm to 0.4mm / 1500-8000
x 10-5 SI;
0-200, where epidote altered / occurs throughout district at elevations above 300m
Hornblende-plagioclase phyric andesite / massive;
porphyritic and glomeroporphyritic;
holocrystalline locally (microdiorite to microgabbro) / 15-40% plg, 0.5-2mm;
3-7% hbl, 1-4mm, up to 1cm, with oxidized rims to 0.3mm wide;
local opx, cpx and ol;
Phenos = 20-50% of rock / plg microlaths, hbl to 0.2mm & micro- to cryptocrystalline material; holo-crystalline locally / An 80 to 45
core to rim, local cores to An 98 / 3-5% mt and ilm in groundmass and as phenos to 0.6mm; mt:ilm ratios range from 3:1 (phenos) to >7:1 (ground-mass) / 4500-8000
x 10-5 SI / hypabyssal intrusions and dykes within volcaniclastic rock units; the andesite underlies much of the district and forms a 4 by 4 km exposure in the western part of the area
Fine-grained andesite and micro-quartz diorite / massive; fine porphyritic and glomeroporphyritic; holocrystalline locally / 3-10% plg, 0.2-1mm; tr.-5% hbl to 0.2-1mm, up to 2mm; tr-0.5% cpx to 1mm; Phenos 15% of rock / plg microlaths <0.05mm and microcrystalline material, minor hbl and local cpx / An 70 to 40, core to rim / 3-7% mt & minor ilm as phenos 0.1-0.5mm; mt in groundmass / 3000-6500,
up to 12000
x 10-5 SI / intrusions and dykes within volcaniclastic sequence, in Katala and northeastern part of district
Pyroxene-plagioclase phyric andesite / porphyritic and glomeroporphyritic; holocrystalline locally / 25-35% plg, 0.5-4mm;
2-3% cpx, 0.3-3mm;
1-3% ol to 1mm;
Phenos = 30-40% of rock / 25-35% plg; 7-12% cpx, 3-5% mt and microcrystalline material / An 65 to 35, core to rim / 2-3% mt as phenos to 0.3mm and in groundmass / 1500-3000
x 10-5 SI / hypabyssal intrusion in northern part of district, geometry poorly constrained
Abbreviations: An- anorthite component determined by optical and microprobe analyses, cpx-diopside, hbl- amphibole, ilm- ilmenite, mt- magnetite, phenos-phenocrysts, plg- plagioclase, ol-olivine, opx-enstatite. Microcrystalline= <0.02 mm; cryptocrystalline= <0.005 mm. The stated mineral abundances represent visual estimates and are approximate.
Description of andesitic volcaniclastic rock units and andesitic intrusions in the Batu Hijau district.
Description of predominantly equigranular plutonic rocks in the Batu Hijau district.
Rock Type (Map ID) / General Texture / Phenocrysts or Crystals / Groundmass or Interstitial Phases / PlagioclaseComposition / Accessory Minerals / Magnetic
Susceptibility / Field Relationships and Distribution
Hornblende quartz diorite
Sekongkang
(QD1)
Santong
(QD2)
Katala-Batu Hijau (QD3) / ------
hypidiomorphic equigranular and subporphyritic
hypidio- and idio-morphic equi-granular to sub-porphyritic
hypidiomorphic equigranular / ------
50-75% plg, 0.5-3mm; 5-15% qz to 1mm;
5-15% hbl, 1-2mm; local opx & cpx ( up to 5-7%) and bi (<3%)
60-90% plg, 0.2-2mm; 0-10% qz , <0.5mm;
7-10% hbl, 1-3mm
70-85% plg, 1-3mm;
5-15% qz to 1mm;
5-15% hbl, 1-3mm; local opx, cpx and bi / ------
interstitial qz-plg+ksp, 0.1-0.5mm, comprise up to 40% of rock locally
interstitial plg+qz, 0.1-0.2mm, consti-tutes <5% of rock commonly, up to 40% of rock locally
interstitial qz-plg+ksp, 0.1-0.5mm, comprise up to 15% of rock locally / ------
An 60 to 30
core to rim, local An 20 rim o/g
An 80 to 40
core to rim
An 70 to 30
core to rim / ------
2-4% mt and ilm (~1-3mt:1ilm), 0.4-0.8mm; ilm/hm in bi-pyx bearing phases
2-3% ilm and subordinate mt, 0.2-0.6mm
2-3% mt and ilm (mt>ilm), 0.4-0.8mm; ilm/hm in bi-pyx bearing phases
(titanite after ilm, apatite in all QD) / ------
2500-5500
x 10-5 SI
500-5500
x 10-5 SI
2500-5000
x 10-5 SI / plutons and dykes throughout district
intrudes andesite and volcanic lithic breccia; grades into porphyritic & tonalitic phases locally
intrudes andesite and volcaniclastic rock units;
includes micro-quartz diorite & diorite locally
intrudes andesite and volcaniclastic rock units; composite pluton that intrudes po tonalite in Katala and po dacite in Batu Hijau
Granodiorite / hypidiomorphic equigranular / 35-50% plg, 1-2mm;
35-50% qz to 1mm;
7-10% ksp to 1mm;
3-7% hbl/bi to 1mm / interstitial ksp-qz, 0.1-0.5mm, comprise less than 10% of rock / An 40 to 30
core to rim / 1% ilm and tr. mt;
rare apatite / 500 x 10-5 SI / late dykes in Katala; marginal to equigranular hbl quartz diorite (QD3)
Tonalite to Granodiorite / hypidiomorphic equigranular to porphyritic; graphic
qz-plg intergrowth / 15-50% plg , 1-4mm;
20-40% qz to 1mm, local qz eyes to 5mm;
3-5% bi to 1mm / interstitial qz-plg, & lesser ksp, 0.05-0.4mm , comprise 10-40% of rock / An 55 to 25
core to rim / 1-3% pyrite (after ilm or magnetite?) ; tourmaline in cavities
rare apatite / <100 x 10-5 SI / late dykes in Sekongkang; forms intrusive breccia with clasts of QD1 and andesite
Notes: 1) bi-pyx+hb-bearing equigranular quartz diorite in Katala and Sekongkang associated with adjacent bi-pyx hornfelsic andesite and volcaniclastic rocks.
2) Abbreviations: An- anorthite component determined by optical and microprobe analyses, ap- apatite, bi- biotite, cpx- diopside, hbl- amphibole, ilm- ilmenite, ilm/hm- lamellar hematite in ilmenite, mt- magnetite, o/g- overgrowth, opx- enstatite, plg- plagioclase, po- porphyritic, pyx- pyroxene, qz- quartz, tt- titanite. Mineral abundance estimates are approximate.
Description of porphyritic plutonic rock types in the Batu Hijau district.
Rock Type / General Texture / Phenocrysts / Groundmass / PlagioclaseComposition / Accessory Minerals / Magnetic
Susceptibility / Field Relationships and Distribution
Porphyritic
hornblende tonalite / strongly porphyritic; aplitic groundmass / 15-30% plg, 1-3mm, up to 8mm;
3-7% hbl, 1-5mm;
tr.-2% resorbed qz eyes to 2mm;
local bi (1-2%) to 1mm;
minor relict opx, <2mm;
(hbl ranges up to 12% at Arung Ara);
Phenos=20-40% of rock / allotriomorphic- granular plg-qz, 0.05-0.2mm ;
locally includes ksp (2-3%), bi (2-3%) and rare hbl / An 70 to 35
core to rim,
reversely zoned at Katala / 2-4% mt and ilm, 0.4-1mm, mt:ilm ratio >4:1;
ilm altered to titanite;
minor apatite / 2000-5000
x 10-5 SI / small plutons and dykes at Katala and Arung Ara; po tonalite intrudes QD2 at Arung Ara and is intruded by QD3 at Katala
Porphyritic
dacite / porphyritic, but to a lesser extent than other porphyritic intrusions / 10-30% plg, 0.5-3mm, 1mm most common;
3-10% hbl, 1-2mm;
1-5% bipyramidal qz eyes to 1.5mm; trace bi;
Phenos=15-40% of rock / allotriomorphic-granular plg-qz, <0.01mm / An 50 to 30
core to rim / 2-3% mt as phenos, 0.2-1mm, and in groundmass, <0.05mm ; mt alter. to hm & titanite;
minor apatite / 1500-3000
x 10-5 SI / lone stock and NE dykes at Batu Hijau, where it intrudes andesite and volcaniclastic rocks and is intruded by QD3 and tonalite porphyries
Tonalite porphyry complex / strongly porphyritic, aplitic groundmass / 25-45% plg, 1-8mm;
<1-7% hbl, 2-8mm;
tr.-7% resorbed qz eyes to 10mm; minor cpx;
1-2% bi books to 4mm;
Phenos=35-60% of rock / allotriomorphic-granular plg-qz, 0.05-0.3mm;
minor bi within groundmass of Young Tonalite / An 50 to 35,
core to rim;
An 20 rim o/g in Young Tonalite / 1-2% mt octahedra to 2mm; rare ilm;
mt in groundmass, 0.05-0.2mm; apatite; titanite rims to mt / 2000-3000
x 10-5 SI / stocks and NE-trending dykes in Batu Hijau; more than three phases; description biased towards least-altered Young Tonalite
Porphyritic andesite / Porphyritic, aplitic to micro-crystalline groundmass / 10-30% plg, 0.5-4mm;
5-15% hbl, 0.5-4mm;
local cpx, <3% and <1.5mm ; local qz eyes to 3mm;
Phenos=15-30% of rock / plg microlaths, 0.02-0.2mm, and 3-10% allotriomorphic qz, <0.3mm; minor hbl, 0.05-0.2mm, & 0-3% interstitial ?ksp / An 70 to 40
core to rim / 3-5% mt and ilm as phenos, 0.2-0.5mm (>3mt:1ilm); mt in groundmass; apatite;
local titanite-?hm alt. of ilm / 3000-5000
x 10-5 SI / narrow dykes (2-50m), commonly 10-15m at Santong, Batu Hijau and Katala; includes dacite and quartz diorite phases
Mineral abbreviations: An- anorthite component, bi- biotite, cpx- diopside, hbl- amphibole, ilm- ilmenite, ilm/hm- lamellar hematite in ilmenite, ksp- K-feldspar, mt- magnetite, o/g-overgrowth, opx- enstatite, plg- plagioclase, pyx- pyroxene, qz- quartz. Microcrystalline= <0.02 mm; cryptocrystalline= <0.005 mm. Other abbreviations are indicated in Tables 1a and 1b. The stated mineral abundances represent visual estimates and are approximate.